The central nervous system (CNS) and the brain in particular, perform the most complex and essential processes in the human body. Surprisingly, contemporary health care lacks sophisticated tools to objectively assess their function. A patient's mental and neurological status is typically assessed clinically by an interview and a subjective physical exam. The clinical laboratory currently has no capacity to assess brain function or pathology, contributing little more than identification of poisons, toxins, or drugs that may have externally impacted the CNS. Brain imaging studies, such as computed tomography imaging (CT), magnetic resonance imaging (MRI), though widely used and useful, are structural/anatomical tests revealing little or nothing about brain function. In the immediate time of acute brain injury, stroke, or seizure, imaging studies typically reveal no abnormality, even when there is clear and dramatically abnormal brain function. CT and MRI only detect the condition after the morphology or structure of the brain has changed. In some cases it can take from hours to days after the patient is present in an emergency room (ER) before overt changes are evident on the CT or MRI, and before severe neurological pathology is visible. Electrical activity of the brain, however, is affected immediately. New imaging modalities such as functional MRI (fMRI) measure the changes in oxygen saturation in different parts of the brain. Radioisotope imaging such as positron emission tomography (PET) and single photon emission computerized tomography (SPECT) assess chemical changes within the brain as a measurement of function with limited sensitivity and specificity. All of these assessment tools play an important role in selected cases, but they are costly, not universally available, and they do not provide critical information at the early stages of acute care situations. None of the current techniques provides the immediate, actionable information critical to timely intervention, appropriate triage, or the formulation of an appropriate plan of care.
The CNS and brain, of all organs in the human body, are also the most time sensitive and have the least capacity for repair. Currently, emergency room patients with altered mental status, acute neuropathy, or head trauma must undergo costly and time consuming tests to determine an appropriate course of treatment. Unfortunately, in many cases, the clinical condition of patients continue to deteriorate as they wait for equipment to become available or for specialists to interpret tests. The task of the ER physician is to basically establish whether the brain is functioning normally, whether the abnormality is psychiatric or organic in nature, whether an organic abnormality is global or lateralized, and to develop an initial assessment of the diagnostic possibilities. The problem that faces ER physicians is that their resources are quite literally limited to a flashlight and a rubber reflex hammer. Amazingly, all of the physician's decisions concerning the administration of emergency treatment or intervention, including CT scan, spinal tap, additional consultation or discharge are based on the results of this simplistic exam.
Often, ER patients are sent for imaging studies, yet many functional brain abnormalities, such as seizure, are not visible on a CT scan. Some abnormalities which will eventually have anatomical and structural consequences often take time to become visible. This is true for many important conditions such as ischemic stroke, concussion, raised intracranial pressure, and others. Thus, while the location, expense, and limited availability of the CT scan can be problematic, so indeed can the fact that it is a structural as opposed to functional test.
One-third of over 200 physicians surveyed at the American College of Emergency Physicians feel that the combination of a good clinical laboratory, a neurological exam, and a CT scan of the head, is not adequate for the assessment of every patient with altered mental status or neurological dysfunction. Consensus estimates from the CDC NHS database and practicing ER physicians, is that patients requiring a mental status exam represent 15% of the more than 100 million ER visits annually in the U.S., and in some institutions, considerably more.
There are more than 100 million ER visits per year in the US alone (CDC/NCHS) database. In year 2000, more than 13 million of these patients required a formal mental status exam and nearly 5 million had CT scans. This data indicates the need for real-time functional brain state assessment which can be performed in the hospital, in an ambulance, at a sporting event, or any other location where acute neurological evaluation may be necessary.
All of the brain's activity, whether reflexive, automatic, unconscious, or conscious, is electrical in nature. Through a series of electro-chemical reactions, mediated by molecules called neurotransmitters, electrical potentials (voltages) are generated and transmitted throughout the brain, traveling continuously between and among the myriad of neurons. This activity establishes the basic electrical signatures of the electroencephalogram (EEG) and creates identifiable frequencies which have a basis in anatomic structure and function. Understanding these basic rhythms and their significance makes it possible to characterize the EEG as being within or beyond normal limits. At this basic level, the EEG serves as a signature for both normal and abnormal brain function.
The electrical activity of the brain has been studied extensively since the first recordings over 75 years ago, and especially since the advent of computers. “Normal” electrical activity of the brain has been well characterized in hundreds of studies, with a narrow standard deviation. The frequencies of electrical activity of some parts of the brain are the normal response to various stimuli, such as acoustic, visual, or pain, known as “evoked potentials.” Evoked potentials (EP) are particular waves that have characteristic shapes, amplitudes and duration of peaks within those wave shapes, and many other features, all of which have well established normative data, generated over decades of research. Normative data for all of the EEG and evoked response waves are remarkably constant across different genders, ages, and ethnicities. Moreover, any variability that does exist is well described and explained.
Neuroscientists have also characterized the EEG signature of various different brain pathologies. Just as an abnormal electrocardiogram (ECG) pattern is a strong indication of a particular heart pathology, an irregular brain wave pattern is a strong indication of a particular brain pathology. A wide array of pathologies have been well characterized: acute and chronic, structural, toxic, metabolic, and even specific diagnoses such as: ischemic stroke, epileptic seizures, concussion, alcohol, and drug overdose, psychiatric conditions, and dementias including Alzheimer's disease. A large body of data, with continuing refinements and contributions, constitutes the field of clinical neurophysiology.
Even though EEG-based neurometric technology is accepted today and a tremendous body of data exists, application in the clinical environment is notably limited. Some of the barriers limiting its adoption include: the cost of EEG equipment, its lack of portability, the need for a technician to administer the test, the time it takes to conduct the test, and the need for expert interpretation of the raw data. More importantly, the technology is neither available nor practical in the acute care setting, especially at the point of care. A complete diagnostic EEG instrument typically costs $80,000, fully equipped. Despite the high costs, the instrument produces essentially raw waveforms which must be carefully interpreted by an expert. Moreover, use of the standard EEG equipment remains extremely cumbersome. It can take 30 minutes or more to apply the required 19 electrodes. Once the patient is prepared for the test, the recording itself can take from 1 to 4 hours. Data is collected and analyzed by an EEG technician, and are then presented to a neurologist for interpretation and clinical assessment. There are some self-standing dedicated neurodiagnostic laboratories which focus strictly on detailed analysis of electrical brain data. Neither the specialized centers, nor the typically large hospital EEG machines are practical for the ER, operating room (OR), intensive care unit (ICU), or any other acute care medicine setting where patients are in the greatest need. Immediate, functional brain state assessment is needed to treat patients with acute neurological injury and disease for the prevention of further damage and disability.